1. Field of the Invention
The present invention relates to a vacuum processing apparatus with a vacuum pump, in which products of reaction in exhaust gas can be prevented from adhering to the inside of the vacuum pump so that the maintenance operation is easier, although the conductance of an exhaust pipe system is lowered so that a trap unit and the vacuum pump can be reduced in size.
2. Information of the Related Art
In manufacturing processes for semiconductor devices, a semiconductor wafer (hereinafter referred to as "wafer") is subjected to various processes, such as CVD, etching, ashing, etc., using process gases in a vacuum. In these vacuum processes, exhaust gas that contains products of reaction and unaffected process gases, based on reactions of the process gases, is discharged through an exhaust pipe system in a process chamber. If unwanted by-products, such as the reaction products, unaffected gases, etc., adhere to the inside of the exhaust pipe system, however, exhaust pipes, valves, and vacuum pump must be cleaned. The cleaning of the exhaust pipe system involves troublesome operations, including removal of the exhaust pipes, valves, and vacuum pump and cleaning of the pump. If the reaction products are corrosive, moreover, the exhaust pipes or the like may possibly be corroded, so that adhesion of the reaction products to the exhaust pipe system must be minimized.
Conventionally, a vacuum processing apparatus is constructed in the manner shown in FIG. 4, in order to prevent the reaction products and other unwanted by-products from adhering to the exhaust system. In FIG. 4, numeral 1 denotes an airtight process chamber, which contains a wafer stage 11, having a heater therein, and a process gas inlet portion 12. The process chamber 1 is connected with an exhaust pipe 15, which is provided with a drag pump 13 and a dry pump 14. Thus, the exhaust pipe system is arranged so that after the process chamber 1 is first evacuated through a branch line 16 to a predetermined degree of vacuum by means of the dry pump 14, it can be further evacuated to a higher degree of vacuum by means of the drag pump 13.
A trap 17 is provided on the upstream side of the drag pump 13, and heating means, e.g., a tape heater, is wound around that portion of the exhaust pipe system between the exhaust port of the process chamber 1 and the trap 17. According to this arrangement, the exhaust pipe 15 can be heated to prevent the adhesion of the reaction products, and the reaction products can be cooled to a temperature lower than their sublimating points and compulsorily separated in the trap 17. Thus, the reaction products can be prevented from adhering to the exhaust pipe system on the downstream side. In FIG. 4, symbols Va, Vb and Vc designate valves.
Since the trap 17 is located on the upstream side of the drag pump 13, however, the apparatus with the above-described construction involves the following problems.
Since the trap 17 is subject to a substantial exhaust loss, the conductance of the exhaust pipe 15 must be increased, and the diameter of the pipe 15 is adjusted to about 4 to 8 inches, for example. Accordingly, the trap 17 and the drag pump 13 are expected to be large-sized. If the trap 17, which should be cleaned periodically, is located on the upstream side of the drag pump 13, water remaining in the cleaned trap 17 may possibly flow into the process chamber 1, thereby corroding the elements in the chamber 1 or exerting a bad influence on the process of a wafer W.
Accordingly, the inventors hereof intend to solve the above problems by locating the trap 17 on the exhaust side (downstream side) of the drag pump 13. To attain this, an arrangement is proposed such that a tape heater, for example, is wound around the drag pump 13, as well as the exhaust pipe, and products of reaction are passed in a gaseous phase through the pump 13.
In the drag pump 13, a rotor unit is located in a casing, which is provided with a water cooling jacket, and a distributor is located on the casing side so as to surround the rotor unit. The process chamber 1 is evacuated as the rotor unit is rotated. Even though the tape heater is wound around the casing, therefore, heat is absorbed by the water cooling jacket and the distributor, so that it cannot be easily transferred to the rotor unit. Thus, it is difficult to heat the rotor unit to a temperature of, for example, about 120!n, which is higher than the separation temperature of the reaction products.
It is hard for a conventional tape heater to heat the casing to a temperature such that the rotor unit temperature is increased to the aforesaid level. Accordingly, a special resistance heating element must be used to attain this, entailing substantially increased power consumption. If the casing is heated to too high a temperature, moreover, a sealing member of the drag pump will inevitably be degraded. In consequence, the casing temperature should not be increased excessively.
Even though the interior of the exhaust pipe and the inner wall of the casing are heated to a temperature high enough to prevent the adhesion of the products of reaction, therefore, the rotor unit cannot be heated to this temperature level, so that the reaction products adhere to the rotor unit, thus requiring frequent maintenance operation for the drag pump.